This invention relates to positive feed power drills having a spindle drive gear train and a spindle feed gear train arranged to be driven by the same motor, and having means for positively stopping the spindle feed until manually placed in a retract mode for reversal of the positive feed drive, and more particularly to a system for ratcheting a feed coupling gear after the spindle has been advanced to a positive stop, thereby allowing the spindle to continue to be turned, but not further advanced, until it is retracted.
Positive feed power drills normally have a single motor for turning a spindle through a drive gear train. The spindle is threaded into a feed gear that turns for advancing the spindle as the drill progresses through a work piece. The feed gear is driven by a gear train from the same motor as the drive gear train, but the gear ratio of the drive gear train is selected to be slightly less than the gear ratio of the feed gear train so the feed gear will turn slightly faster than the drive gear. In that way, the spindle is advanced a predetermined amount for each turn through the work piece.
Once the spindle has been advanced sufficiently, it has been the practice to provide manual means to disengage the spindle feed gear train from the drive gear train and lock it in place. As the motor continues to drive the spindle in the same direction, the spindle threads turn inside the locked feed gear to automatically reverse and therefore retract the spindle. Once the spindle has been retracted, the actuatable means is reset for another drilling or countersinking cycle. For some applications, as in blind drilling where the depth has to be accurately controlled, or in countersinking applications, it is an object of this invention to simply provide a positive stop for the spindle, and allow a feed coupling gear to ratchet until such time as the retracting means is manually actuated to reverse the positive feed, and thus retract the spindle for another drilling or countersinking cycle.
The stop control feature of the present invention is practiced in a positive feed power drill having a threaded spindle passing through an internally threaded feed gear, a drive gear slidably locked onto the spindle, a drive gear train extending from a drive motor through a coupling gear to the spindle drive gear to turn the spindle at a rate set by the motor through this gear train, and a spindle feed gear train extending from a coupling gear to the spindle feed gear. The spindle feed coupling gear is releasably locked to the spindle drive coupling gear by side teeth for turning the spindle feed gear train as the spindle drive gear is turned by the motor. The gear ratios for the two trains are selected to drive the spindle feed gear at a faster rate than the spindle drive gear.
The feed coupling gear is mounted with a bearing on the same shaft that the drive coupling gear is mounted, but the feed coupling gear is mounted with a bearing on a flange integral with the shaft so that the shaft may be moved axially to uncouple the side teeth of the feed coupling gear from the drive coupling gear. A hydraulic piston is arranged at the bottom of the shaft for so raising the shaft on its axis, against the force of a compression coil spring over the coupling gear, as to raise lower side teeth of the feed coupling gear out of engagement with upper side teeth of the drive coupling gear, and raise upper side teeth of the spindle feed coupling gear into locking engagement with fixed teeth on the gear train housing while the spindle drive gear train continues to rotate. That reverses the relative rotation of the spindle in the feed gear so that the spindle is rapidly retracted. Hydraulic pressure is provided to the piston through a passage in the gear housing when a valve stem is manually actuated to a second position by means associated with the spindle after the spindle has been advanced to the positive stop.
Once the spindle is retracted, the valve stem is released so that it automatically returns to its first position. This removes the hydraulic pressure which actuates the piston, allowing the spring to force the feed coupling gear away from the fixed teeth on the gear train housing and toward the drive coupling gear for re-engagement of lower side teeth of the feed coupling gear with upper side teeth of the drive coupling gear, thereby recycling the tool for another drilling or countersinking operation, unless the drive motor is manually turned off.